Update 5:30 am Addition of a second patent concerning the AirPods Max
On September 12, Patently Apple released an IP report titled “Apple last week won a major patent for spatial audio covering Head-Linked Transfer Function (HRTF) maps.” Today, the US Patent and Trademark Office officially granted Apple a second patent relating to spatial audio and head-related transfer function (HRTF) settings. A second patent issued today concerns AirPods Max with head detection.
Apple notes in its patent filing that a sound emitted by a discrete sound source travels to a listener along a direct path, for example, through air to the entrance to the ear canal of the listener, and along one or more indirect paths, for example, by reflecting and diffracting around the head or shoulders of the listeners. As sound travels along indirect paths, artifacts can be introduced into the acoustic signal that listeners’ ears receive. These artifacts are anatomically dependent and, therefore, are user specific.
In addition, user-specific artifacts provide the listener with clues to locate the source of the sound. User-specific artifacts are characteristics of sound transmission that can be encapsulated in a Head Related Transfer Function (HRTF) data set. A single HRTF in the dataset is a pair of acoustic filters (one for each ear) that characterize the acoustic transmission from a particular location in a reflection-free environment to microphones placed in a listener’s ears. A dataset of HRTFs contains the fundamental clues pursued by a listener to locate sounds.
A listener can use simple stereo headphones to create the illusion of a sound source somewhere in a listening environment by applying an HRTF to a binaural simulation of the sound source. HRTF can relate to the particular location or direction of the sound source. That is, when a relative position between the user and the location of the sound source is known, an HRTF for the relative position can be selected from the HRTF data set and applied to binaural simulation of the sound source to better simulate the sound source. . Therefore, the HRTFs are selected based on the direction of the sound source relative to the listener.
Because HRTFs are highly individualized, binaural simulation using non-individualized HRTFs (for example, when a listener auditions a simulation using another person’s HRTF dataset) can cause audible issues. both in the perceived position and the quality (timbre) of the virtual sound. As such, an HRTF that effectively simulates a sound source at a location relative to a first user may not effectively simulate the sound source at the same location relative to a second user. That is, the first user can experience the simulation as a realistic rendering, but the second user cannot.
Existing methods of generating individualized head-related transfer functions (HRTFs) are time consuming or impractical to incorporate into consumer electronic devices that perform binaural simulations. When individualization of HRTF is impractical or impossible, a generic HRTF can be used instead. Generic HRTF can represent a composite HRTF of a group of people. For example, generic HRTF may have user pool mean values for one or more underlying parameters, such as inter-atrial time difference (ITD), inter-atrial level differences (ILD), and diffuse field HRTF (DF-HRTF).
The Apple patent covers an audio system and a method of using the audio system to determine a user-specific head-related interaural transfer function (HRTF) parameter is described. By replacing or adapting generic HRTF parameters with user-specific HRTF parameters, an individualized HRTF can emerge. For example, an average ITD of a generic HRTF can be replaced with a measured ITD of a particular user to individualize the HRTF data set for the user. When a sufficient number of the underlying generic HRTF parameters are customized, the composite HRTF data set should be indistinguishable from a measure of the user’s individualized HRTF.
Apple’s patent FIG. 1 below is an illustrated view of a user listening to an audio system; FIG. 3 is a flowchart of a method for determining a head-related interaural transfer function (HRTF) parameter; and fig. 4 is a pictorial view of a user in a pseudo-anechoic environment.
As you can imagine, Apple’s spatial audio patent 11,190,896 is full of details that you can check out here.
Helmet with head detection
Apple got another patent for the headphones, this time mainly related to AirPods Max, titled “Headsets with over-the-head detection.” More specifically, the different features help to improve the overall user experience by incorporating a range of sensors and new mechanical features into the headphones.
The patent granted by Apple includes several different features suitable for use in the circumaural and on-ear headphone designs. Designs which improve user comfort and improve user control of the headphones are discussed. Various configurations of sensors and positions of electronic components are also discussed. Comfort-of-use features that include detachable cushions and automatic headphone donning and doffing detection are also discussed.
Apple issued patent 11,190,878 is a long and in-depth issued patent that you can view here.